Extreme ivory poaching led to defenseless elephants in Mozambique | NOVA
Mozambique’s devastating civil war, fought between 1977 and 1992, appears to have had unintended consequences: the rapid evolution of defenseless elephants.
Both sides of this war were financed largely through the ivory trade, fueled by the rapid slaughter of Mozambican elephants. In just 15 years, elephant populations in Gorongosa National Park have declined by 90%. In the early 2000s, there were only 200 elephants in the whole country, reports Nature. Among them were individuals who, thanks to a rare genetic mutation, lacked defenses. Without ivory to offer, they were more likely to be spared and survive to pass on their lack of tusks to their offspring.
Since the end of the war, park observers have noted an increase in the number of elephants without tusks. A study published today in the journal Science delves deep into the elephant genome to show another unexpected way that human affairs can shape our biological world. “It’s more than numbers,” Rob Pringle, an environmentalist at Princeton University and co-author of the study, told The Guardian. “The impacts people have, we are literally changing the anatomy of animals.”
The study authors began by analyzing historical video footage from before the Civil War and contemporary elephant sighting data kept by local NGOs. These data showed that the dramatic decline in elephant populations in Gorongosa meant an equally dramatic increase in the proportion of surviving tuskless female elephants. While at the start of the war, defenseless females made up 18% of the park’s female population, they now make up more than half, and about a third of female elephants born after the war were defenseless. In total, the authors estimate that over the 28-year period analyzed by the study, defenseless females were about five times more likely to survive than defenseless individuals.
The researchers then delved into the selection mechanism by observing that there was no evidence of defenseless male elephants in the park. They hypothesized that any evolutionary mechanism acting on Gorongosa’s defenses is likely to be a “dominant and fatal trait linked to the X chromosome”. This means that the mutation would be transmitted exclusively by female elephants, with only one copy needed to cause defenses in females and defenseless male elephants dying in utero. If this were to be the case, helpless mothers in the park would be much more likely to give birth to daughters. The data confirmed this hypothesis. In the first decade after the war, they found that the tuskless rates among war surviving elephant descendants remained at a rate almost twice that of pre-war populations. . And not only that, but they found that helpless mothers gave birth to almost 66% of daughters.
Finally, the authors moved on to a more detailed genomics to try to determine the exact genes responsible for this wave of absence of defenses. Comparing whole genome scans of 18 Gorongosa elephants with and without tusks, they focused on mutations in two possible genes: AMELX and MEP1a, both of which play important roles in tooth development in many mammals. AMELX is even associated with a similar “X-linked dominant male-lethal” syndrome in humans, which restricts the growth of our lateral incisors, our defensive counterpart.
There are many precedents for the kind of rapid change the study authors advocate in Gorongosa. Bighorn sheep in Alberta, Canada; crickets in Hawaii; and Caribbean lizards have all shown remarkably rapid transformation in response to evolutionary pressures. Yet to see a trait like the absence of tusks evolve in less than two decades, in a “long-lived, slow-breeding species like the elephant, is incredible,” John Poulsen, a tropical ecologist at the University. Duke who did not participate in the study. , told The Atlantic.
And Gorongosa is not the first place where elephants at high poaching risk have strayed from tusks. New Scientist reports that less than 5% of Asian elephants in Sri Lanka still have tusks. Atlantic notes that in South Luangwa National Park in Zambia, the percentage of female elephants without tusks increased from 10% to 38% between 1969 and 1989. And in Addo National Park in South Africa, 98 % of female elephants are now believed to be defenseless, a percentage that researchers argue cannot be explained simply by the region’s vegetation or selective hunting.
But identifying the exact genetic mechanisms at play and differentiating them from other pressures like climate change is always difficult in studies like this, said Chris Darimont, a conservation scientist at the University of Victoria in Canada, who does not did not participate in the study. Nature. “It is difficult to prospect for these genes. Moreover, he added, there is a long-standing controversy over whether the pressure of harvesting, like hunting, matters in the first place. Still, he called the genomic data offered in the new study “compelling”, saying the findings should serve as “a wake-up call in terms of empowering humans as the dominant evolutionary force on the planet.”
A loss of tusks is not just a loss for elephants. Elephant tusks are “essentially a Swiss army knife for African elephants,” Pringle told New Scientist, helping them strip trees of bark, dig holes, find water. And many other animals indirectly depend on these tusks, munching on insects from trees without bark or drawing water from these holes. “It’s what maintains biodiversity,” co-author Shane Campbell-Staton, evolutionary biologist at Princeton University, told New Scientist. “There are all these cascading consequences that can result from our actions which are quite surprising. “
With proper ecological protections in place, the lack of defenses will gradually disappear in Gorongosa, Pringle told The Guardian. “We actually expect this syndrome to decrease in frequency in our study population, provided the conservation picture remains as positive as it has been recently,” he said. “There is such a blizzard of depressing news about biodiversity and humans in the environment and I think it’s important to stress that there are positives to this picture.”